1. Field of the Invention
The invention relates to the field of fluid application in a pattern to fibrous webs, and particularly to applying bonding materials or adhesives in fluid form to a soft, absorbent fibrous web, such as sanitary paper, by way of an intaglio roll.
2. Description of the Prior Art
In making nonwoven fibrous products, and to an increasing extent paper products, bonding materials or adhesives are added to the webs to strengthen them. Examples of adhesively bonded paper products for which the invention is applicable are disclosed in U.S. Pat. No. 3,821,068 and British Pat. No. 1,294,794. Typically, the adhesive is applied to the web with conventional printing apparatus, in which the adhesive is applied in fluid form to gravure or intaglio rolls, which are in turn rotated into contact with a passing fibrous web to which the adhesive is applied in the pattern of the fluid carrying recesses in the surface of the intaglio roll. However, conventional printing apparatus have not been entirely satisfactory due to their shortcomings in handling fluids which are more viscous (up to 600 CPS, for example) and more subject to deterioration than the inks for which the apparatus were designed. Additionally, being designed to print upon coated or sized paper, conventional printing apparatus are unable to control the loose fibers which are inadvertently picked from the soft, absorbent fibrous webs by the intaglio roll and carried into the fluid application zone. Even the use of conventional trash doctors positioned against the intaglio roll at a position beyond where the roll contacts the web and before the fluid application station are not entirely effective, because the fibers are carried in the fluid carrying recesses past the trash doctor.
One form of conventional printing apparatus is illustrated in U.S. Pat. Nos. 1,812,884; 2,338,561; 2,371,223; and 2,631,532. In that form of apparatus, the fluid is applied to the intaglio roll by rotating the roll through a large open bath of the fluid. The "open bath" type of applicator is not satisfactory for the application of adhesives to soft, absorbent fibrous webs, because the adhesives are deteriorated by excess exposure to air in the large bath and because loose fibers from the web accumulate in the bath of fluid and substantially increase the apparent viscosity of the fluid which reduces the ability to apply the fluid uniformly without fiber contamination to all fluid carrying recesses.
Another form of conventional printing apparatus is disclosed in U.S. Pat. Nos. 2,177,656 and 3,641,932. In that form of apparatus the fluid is applied through a pressurized fountain against a small zone of the rotating intaglio roll. The "fountain type" apparatus can be undesirably sensitive to the angle of application and velocity of the fluid applied to the intaglio roll.
An additional form of conventional printing apparatus is described in U.S. Pat. Nos. 2,655,102 and 3,630,146 and consists of a small reservoir of fluid positioned against the downwardly moving surface of the intaglio roll. This form of apparatus does not have the ability to prevent loose fibers from accumulating in the fluid.
Another form of conventional printing apparatus is a modified fountain arrangement in which the fluid is pumped under pressure through a long conduit-like zone against the intaglio roll. Illustrations of this form of apparatus can be found in U.S. Pat. Nos. 2,376,620 and 2,573,336. It has to a large degree the same shortcomings as the "fountain type" apparatus.
In addition to the above-stated shortcomings of the prior art conventional printing apparatus for use in applying adhesives to soft, absorbent fibrous webs, the prior art apparatus have difficulty uniformly filling all fluid carrying recesses with adhesives without leaving excess adhesive on the surface of the intaglio roll. This difficulty is due to such causes as uneven spreading of fluid across the width of the intaglio roll and turbulent flow of the fluid against the intaglio roll, both of which increase at the high speeds desirable for commercial operation.
In view of the shortcomings of the prior art, it is an object of the invention to provide an improved method and apparatus for applying adhesive fluid to an intaglio roll for transfer to a soft, absorbent fibrous web at high speeds without the above-described disadvantages.